An audiotape of the conversation appeared on the Internet and opened a window into American handling of the political crisis here, as the two diplomats candidly discussed the composition of a possible new government to replace the pro-Russian cabinet of Ukraine’s president, Viktor F. Yanukovych. It also turned the tables on the Obama administration, which has been under fire lately for spying on foreign leaders.

The developments on the eve of the Winter Olympics opening in Sochi, Russia, underscored the increasingly Cold War-style contest for influence here as East and West vie for the favor of a nation of 45 million with historic ties to Moscow but a deep yearning to join the rest of Europe. The tit for tat has been going on since November, when Mr. Yanukovych spurned a trade deal with Europe and accepted a $15 billion loan from Moscow. Months of street protests have threatened his government, and American officials are now trying to broker a settlement — an effort the Kremlin seems determined to block.

The posting of the audiotape represented a striking turn in the situation. It was put anonymously on YouTube on Tuesday under a Russian headline, “Puppets of Maidan,” a reference to the square in Kiev occupied by protesters, and then posted on Twitter on Thursday by a Russian government official who called it “controversial.”

The tape captured a four-minute telephone call on Jan. 25 between Victoria Nuland, the assistant secretary of state for European affairs, and Geoffrey Pyatt, the ambassador to Ukraine, trading their views of the crisis, their assessments of various opposition leaders and their frustrations with their European counterparts they see as passive. At one point, Ms. Nuland used an expletive to describe what should happen to the European Union, a comment for which she apologized Thursday.

The two were discussing Mr. Yanukovych’s offer to bring two opposition leaders, Arseniy P. Yatsenyuk and Vitali Klitschko, into the government as prime minister and deputy prime minister. The Americans clearly favored Mr. Yatsenyuk, a former economics minister, and Ms. Nuland said Mr. Klitschko, a former world heavyweight boxing champion, should not go into government. “I don’t think it’s a good idea,” Ms. Nuland said.

Mr. Pyatt expressed hope for a deal to form a new government but warned that Moscow would try to undo their negotiations. “If it does gain altitude, the Russians will be working behind the scenes to torpedo it,” he said.

A link to the secret recording was sent out in a Twitter message on Thursday by Dmitry Losukov, an aide to Russia’s deputy prime minister, just as Ms. Nuland was in Kiev meeting with Mr. Yanukovych and opposition leaders. The White House pointed to that as an indication of Russian involvement, although it said it was not accusing Moscow of taping the call. “I think it says something about Russia’s role,” said Jay Carney, the White House press secretary.

Jen Psaki, a State Department spokeswoman, said she had no information about who posted the recording but criticized Moscow for promoting it. “Certainly, we think this is a new low in Russian tradecraft,” she said.

Mr. Losukov, responding to messages from a reporter on Twitter, rejected the American assertion that he was the first to disseminate the recording. “Disseminating started earlier,” he wrote, adding that his post was being “used to hang the blame” on Russia. Asked if Russia had any role, he said: “How would I know? I was just monitoring ‘the Internets’ while my boss was off to a meeting with the Chinese leader.”

The secret tape, reported Thursday by The Kyiv Post, came to light as a Kremlin adviser, Sergei Glazyev, accused the United States of funding and arming protesters in Kiev and seemed to threaten Russian intervention.

Urging Ukrainian authorities to crush what he described as an attempted coup by American-armed “rebels,” Mr. Glazyev said in an interview published Thursday in a Ukrainian edition of a Russian newspaper that Washington was violating a 1994 agreement by trying to shape events in Kiev. “What the Americans are getting up to now, unilaterally and crudely interfering in Ukraine’s internal affairs, is a clear breach of that treaty,” said Mr. Glazyev, who advises President Vladimir V. Putin of Russia on Ukraine. “The agreement is for collective guarantees and collective action.”

This, he said, gave Russia the legal right to intervene in the crisis. He did not specify what form such intervention might take.

Further inflaming the situation, a Ukrainian protest leader who vanished for a week and then emerged from a forest late last month saying he had been “crucified” gave the first full account of his ordeal on Thursday.

The activist, Dmytro Bulatov, appeared with a Lithuanian doctor to rebut government claims that he had only suffered “a scratch” and to accuse Russian agents and a friend of Mr. Putin’s of having a possible hand in his kidnapping and torture.

“It was so scary and so painful that I asked them to kill me,” Mr. Bulatov said at a news conference in Vilnius, the Lithuanian capital. He described his captors as Russian speakers who were “very professional” in inflicting pain. He said they kept his eyes covered with a mask, beat him constantly, cut off part of his ear and then nailed his hands to a wooden door.

“When they nailed my hands to the door, they said they would leave no marks,” he said. He said he had no proof they were from Russian special services but “from the manner they beat me, they clearly knew what they were doing.”

The Lithuanian doctor attending the news conference said part of Mr. Bulatov’s right ear was missing and he had a deep wound on his left cheek and “multiple bruises on his back and arms.” He did not directly confirm the crucifixion claims but said both of Mr. Bulatov’s hands had wounds, although X-rays had shown no broken bones.

Mr. Bulatov said his captors questioned him closely about links between protesters and the American Embassy in Kiev and about protesters who had broken a fence at the house of Viktor Medvedchuk, the head of a pro-Russia civil society group, Ukrainian Choice, and an old friend of Mr. Putin’s.

Mr. Bulatov helped organize the roaming teams that have staged protests outside and, in some cases, tried to break into the homes of Ukrainian leaders and others viewed as close to Russia. He said his captors “made me say that I was an American spy, that I worked for the Central Intelligence Agency” and that American diplomats had given money “to create disorder.”

All of this was untrue, he added, but “I lied because I could not stand the pain.”